Art of rayon manufacture



' a... July 14,1936

UNITED STATES PATENT owner:

muses Aaron-naturism, mm William" Henry Furness, National Park, N. 1., v

. assignor, by means assignments, to New Process Rayon, Inc., a corporation of Delaware I No Drawing. Application February :4, 193 2,

. WHO. 594,961

This invention relates to improvements in the art of rayon manufacture and will be described as applied to the making of cupro-ammoniumsilk in connection with which it is most useful,

I According to my Patent No. 1,770,750, I prepare a cuprpammonium cellulose solution by mixing the copper hydroxide, ammonia and cotten lin-' 01' preparing the solution, the following istrue.

The solution is spun into a caustic soda pre-' ll cipitating bath and the spun thread is withdrawn for subsequent treatment. The thread drawn from the bath carries as part of and with itself, in some form, cellulose, copper hydroxide, and ammonia, and also caustic soda and water. Celt lulose, copper hydroxide, ammonia and water are being introduced into the solution as the.

cuproammonium cellulose solution is spun thereinto. However, less water is spun into the solution than'is removed by the thread. Also more 36 ammonia than is required to keep the cellulose into solution is spun into the bath with the copper ammonia cellulose solution. In consequence of the foregoing, the bath is being deprived of water and being deprived of caustic soda and is' tion,-piping to carry off the overflow, and vessels to receive'such overflow, together with means for effecting recovery such as a still forflthe removal of excess ammonia, and the like.

The operationof such a plant, therefor-are quires the foregoing apparatus as well as a chemical stafl.

By the present invention I propose to maintain the bath constant, e. g., one in which materials a are introduced at the rate withdrawal of such materials by the thread.

- By this process it is necessary to prepare the initial bath but once and, thereafter, the bath will be maintained constant. Provision for cir- 'culation of the bath'is thus eliminatedasis I also the equipment to carry off and receive the I overflow and to recover the constituents thereof. By this elimination it is not necessary to have i a chemical stafl', as will further appear.

' According to another aspect of my invention I 5 propose to dyethe thread as it isspun, thereby greatly simplifying, expediting and cheapening the process of dyeing as will appear.

, The two foregoing inventions may be effectively-used coniointlyas with a constant, 1. e., nonin circulating bathydy eing in the bath can be effectively utilized for otherwise there would be of the dye solution in the overflow of the circulating precipitating bath.

The preferred practice of my invention is as it follows: a

I prepare the solution to be spun in about the following proportions to a batch, namely, 300 pounds of ,cotton linters, 150 pounds of copper hydroxide and 900 pounds of 26 Baum ammeals water. This represents approximately minimum dissolving proportions, the cotton dissolving in about an hour. While the amount of ammonia water specified is that which is required to put the cellulose into, solution, it is more than is required to keep it in solution and, therefore, preferably while the mixer is still running, I abstract 150 pounds of anhydrous ammonia, this being removed preferably by vacuum. The lowering in pressure releases the ammonia as a gas. During removal of the ammonia the temperature is maintained at about 30 C. The solution is then diluted with water to secure the desired concentration of cellulose, preferably about 4%. Y

The solution is now ready to be spun into a precipitating bath-a caustic soda solution. The

"thereinto, the precipitating bath takes on the amounts of copper hydroxide and ammonia per liter Just specified and'reaches a state of equilibrium and thereafter the thread removes cellulose copper hydroxide and ammonia at the rate of in- June 20, 1931.

tion in the precipitating bath is added to the bath by dripping a solution composed of approximately half water and half caustic soda into the bath at a rate with respect to the.caustic soda, equal to the rate of withdrawal of caustic soda by the bath, and with respect to the water at a rate equal to the difference between the amounts of water takenout of the bath by the thread and introduced into the bath with the copper ammonia cellulose solution.

Thus the bath is maintained constant and the solution may be spun thereinto indefinitely without changing the composition of the precipitating bath.

It will be seen from the foregoing that the equipment and staif ordinarily required are elimovement, which bars operate to advance the oncoming thread in the form of a helix continuously moving toward the end of the cage-like drum opposite the end to which the thread is led. The thread is taken oi! said end and wound upon a spool by the usual filer which imparts twist. The sets of bars are so arranged that the diameter of any turn of the thread on the cage is constant so that the tension of the thread isapproximately constant.

While on the cage the thread is treated by acid and, water. There is an acid drip located to discharge on to the cage near the oncoming thread end thereof; a second acid drip is located to discharge on to the cage about mid-way of the length thereof, following which there is a water drip. The cage is inclined and its rate of revolution is such as not to centrifugally discharge the liquids dropped thereon. These liquids run around the cage and also longitudinally thereof toward the oncoming thread end for which purpose the cage is inclined. Sulphuric acid is preferably employed, each drip being of a strength of about 15 grams per liter.

The action of the liquid is first to "decop the thread, removing copper hydroxide ammonia and caustic soda therefrom, and the waterremoves the acid. It will be obvious that the liquids in "running down the cage toward the oncoming thread end, mix. They drip off the cage from said end into a collecting trough and discharge into a tank. Inasmuch as the copper is converted different at one end from what it is at the other.

Sometimes the thread is dyed before put into cloth form. This is done by putting the thread into skein form and the skein is sloshed as des,o4v,4es

scribed. In both cases the dyed product requires repeated washes until the wash water is clear.

I simplify, expedite and cheapen the operation by dyeing the thread as it is precipitated in the bath, andto this end I introduce the dyeing solug tion directly into the bath. This is particularly advantageous with cuproammonium because the caustic soda precipitating bath is one which tends to keep the dyestufi in solution. As the thread which is a gel, is precipitated, the dyeing solution is held in and through the gel matter and the cells thereof. As the thread goes on to the cage and meets with acid the action of the acid precipitates the dye and sets it, the color coming up 1 gradually as decopping progresses. No washing ll other than required to remove the acid is needed and the color is fast. The constant bath above described is particularly useful with this method of dyeing as no loss in dyestuffs occurs such as would be, the case where the ordinariy circulat- 8 ing precipitating bath were employed.

It is, of course, to be preferred that the dyeing solution be introduced at the rate of dye removal by the thread and where dyeing in the bath is resorted to, the proportion of water introduced ll into the bath should be controlled so that no more water is introduced than is being removed.

-In order to keep the constant bath of uniform constituency throughout I prefer to have an internal circulation within thebath itself. It will 3 be obvious that the introduction of the solution to be spun into the bath through the spinneret tends to cause an internal circulation. This result may be furthered by employing a relatively tall, small-'diametred vessel and placing the spinneret ll well toward the bottom thereof, so that the thread is drawn upwardly and over guides located above. In addition the pipes which lead make-up caustic soda and water and the dyeing solution where dyeing in the bath is resorted to, may be extended well toward the bottom of the vessel so as to discharge at that point.

The application of acid to the thread on the cage as above described tends to prevent the deposition of copper on the thread. To prevent deposition of copper on the bars of the cage, the guide which leads the thread on to the cage may have a slight traverse motion so as to prevent the thread from running always over the same surface. This is shown and described in the aforesaid copending application Serial No. 545,761.

It should also be mentioned that the thread, after it has been subjected to the washing liquids, may be dried to the desired extent on the cage, as by means of an internally located heater mechanism over which air is passed in a manner to fiow radially outward through the cage and over the thread as shown and described in said application.

Another advantage of the constant bath of my invention is that it makes it feasible for knitting and weaving mills and the like to manufacture their own rayon with the type of labor ordinarily employed by such mills. No chemical stall is needed because the cuproammonium solution can be prepared and shipped to the mill and the copper hydroxide is precipitated in the form of copper sulphate in the wash liquid and can be obtained by decanting the clear liquor, whereupon the copper sulphate can be returned to the manufacturer of the spinning solution for recovery. Ordinarily the difiiculties are so great in customary practice that it is not feasible for a mill to make its own rayon. 1s 

